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The invention relates generally to pre-fabricated building panels and a method of manufacturing the panels. More particularly, the invention relates to a method of manufacturing pre-fabricated panels wherein the exterior concrete surface is accessible during curing of the concrete and a pre-fabricated panel made from such method.
Pre-fabricated building panels, usually constructed from concrete and studs, have been used to form the walls, floors and roofs of a building structure for many years. Such pre-fabricated building panels act as structural components of the building. Construction utilizing pre-fabricated panels offers many advantages, including more rapid construction and standardization, than traditional on-site construction. Rapid construction allows lower construction financing costs. Pre-fabricated building panels can be constructed on or off-site and then moved into position to form the walls, floors and roofs of the building structure. While pre-fabricated building panels have been frequently used for commercial buildings, they have been less popular for residential use. One reason for their unpopularity for residential use is the difficulty of achieving a wide-range of pleasing textures and colors on the exposed exterior surface of the finished panel. Moreover, buildings constructed of many currently available pre-fabricated panels are restricted in choice of interior wall material. Other reasons for the unpopularity of pre-fabricated building panels for residential construction is the difficulty in providing thermal and acoustic insulation with existing panels. Nevertheless, there remains an interest in housing construction methods which possess the advantages of prefabricated panels. There remains a need, therefore, for pre-fabricated building panels and method of making such panels that can be textured and colored with great variety yet easily and economically.
It is generally believed that the strength of a pre-fabricated building panel increases, inter alia, with the integrity of the bond or connection between the studs and tracks and the concrete panel. A number of methods have been used to increase the integrity of the concrete/stud bond. For the purpose of our discussion, we refer to studs and tracks collectively as studs.
In some pre-fabricated panels, the studs are partially or wholly embedded in the concrete panel. However, such panels are subject to cracking of the concrete due to stresses caused by flexing of the studs. Such stresses are a particular problem where the studs are screwed, but not welded, together or where no metal mesh is used within the concrete. Such panels are also subject to separation between the studs and concrete. The interior walls of buildings constructed of pre-fabricated panels are generally constructed by attaching sheet rock or other type of interior paneling to the studs. Consequently, where the studs are partially or wholly embedded in the concrete, the area in which insulation may be placed is either reduced or eliminated.
Other common techniques for improving the integrity of the concrete/stud bond provide a wide variety of connectors which are attached to the stud and embedded in the concrete. In order to embed the connectors, but not the studs, in the concrete, a stud framework, having connectors extending from the studs, is suspended above a poured concrete panel such that the connectors are embedded in the wet cement. In such manufacturing methods, the exterior face of the panel is face down in the form and, therefore, is not accessible during curing.
One example of a pre-fabricated panel utilizes a reinforcing member which is a metal strip having alternating hooked projections. The reinforcing member is attached to a central portion of a stud and runs along the length of the stud. The hooked projections hook over rods which secure a wire mesh within the concrete. The reinforcing member becomes a part of the stud forming a reinforced structural member. Although the reinforcing member may add additional strength to the studs, it adds significantly to the cost of the structural panel and adds significantly to labor costs due to the need to make extensive connections along the lengths of the studs. Moreover, the reinforcing member adds an unacceptable amount of rigidity thereby increasing risks of cracking of the concrete.
Yet other methods of increasing the strength of the concrete/stud bond employ connectors which are integrally molded into the studs. Such methods utilize specially manufactured studs in which the top flange has been modified to include projections which act as connectors. Such specially manufactured studs, of course, are more expensive then standard xe2x80x9cCxe2x80x9d-shaped and xe2x80x9cIxe2x80x9d-shaped studs.
Other pre-fabricated panels require that a metal framework be first constructed at the job site. The pre-fabricated panels are then attached to the framework. Yet other pre-fabricated panels are constructed of metal mesh and/or rebar reinforced concrete slabs. Such slabs are tilted up into place and attached to the foundation to form the walls of a building. Reinforced concrete slab panels, however, must have a thickness sufficient to support their own weight and the weight of the roof Consequently, reinforced concrete slab panels have thicknesses of at least about four (4) inches, making the panels extremely heavy and difficult to handle. To support the weight of thick reinforced concrete slab panels, the foundation of a building constructed in this manner must also be thicker and heavily reinforced.
Each of the previously described pre-fabricated building panels are not desirable choices for residential construction. First, panels in which the studs are wholly or partially embedded cannot be easily or sufficiently insulated. Indeed, those with wholly embedded joists offer no insulating opportunity because the interior wall boards are attached directly to the exposed stud flange surface. Although some amount of insulation may be placed between wall boards and the interior concrete surface where the studs are partially embedded, the thickness of such insulation is generally limited to about 3 inches or less.
Second, the appearance of the outside concrete surface is severely limited in existing concrete structural panels. For example, those pre-fabricated panels using connectors are usually made in a manner in which the concrete is poured face down in a mold. Because the concrete face of the panel is not accessible during curing, the options for texturing and coloring the face are limited. For example, if it is desired that the face have a color other than the normal color of undyed concrete, dye must be added to the whole of the concrete or the face may be colored after curing. Both of these coloring methods are unnecessarily expensive in view of methods for coloring concrete surfaces during curing. Moreover, post-cure coloring techniques often require an acid etch which involves hazardous chemicals and special handling.
To add texture to the face of panels poured face-down is also unnecessarily difficult and expensive. One way of providing texture to the exterior face of such panels is the use of textured plastic molds. These molds, however, are expensive, driving up the costs of the structural panels significantly. Alternatively, some simple textures may be imparted to the panel face after curing using acid-etching. This technique is also expensive, involving hazardous chemicals and specialized handling requirements. Furthermore, none of these coloring or texturing methods permit one to see how the finished product will look until the result is irreversible. Consequently, if the resulting color or texture is undesirable, the entire pre-fabricated panel must be discarded.
Finally, some of the existing pre-fabricated panels require specially manufactured parts or require extensive labor to manufacture, thereby driving up the costs of the finished panels. Thus, such methods and panels do not provide the anticipated low-cost housing alternative. Moreover, existing pre-fabricated panel systems are generally difficult to assemble into a building at the job site, requiring extensive labor. Yet other existing pre-fabricated panel systems require exceptionally thick foundations or the construction of metal frameworks, all of which significantly increase the cost of construction.
There exists a need therefore for a concrete structural panel and a method of manufacturing the panel which may be insulated sufficiently well for residential use. There exists a further need for a method and panel which permits the exterior face of the panel to be colored and textured economically, safely and with controllable results.
The invention meets these and other needs by providing pre-fabricated structural panels including a concrete slab, a metal mesh embedded in the slab, an insulating panel, one or more studs adjacent to the insulating panel, an upper U-shaped track wrapping around the top edge of each stud and attached to each stud, and a lower U-shaped track wrapping around the bottom edge of each stud and attached to each stud, and one or more connectors hooked over the metal mesh.
The invention also provides a method of making the prefabricated structural panel and a method of constructing a building using the prefabricated panels. These and other aspects and advantages of the invention will be apparent from the description of the embodiments of the invention below.